1. Field of the Invention
The present invention relates to the detection of toxic conditions in biological sludges in biological wastewater treatment systems. More particularly, the invention provides a bioluminescent bacterium for use in detecting toxic conditions in biological wastewater treatment systems.
2. Background Art
The problem of pinfloc formation in wastewater solids can be caused by toxic shock, starvation [caused by high mean cell residence time (MCRT), variable organic loads or influent flow patterns], and/or pump shear (Jenkins, et al., 1993). The transient nature of toxic shock and influent organic loads often renders elucidation of the causative factor difficult. Toxicity of influent wastewater to wastewater solids treatment microbial communities can result in higher operating costs and reduced effluent water quality (Jenkins et al., 1993). Toxic shock causes death of microorganisms and loss of floc structure. The resulting small flocs (pin flocs) settle poorly in downstream clarifiers, and costly polymer addition may be required to meet effluent water quality standards. Effluent violations may result from release of toxicants to receiving waters as a result of loss of specific chemical degrading populations. These effects can be avoided if the incoming waste stream is screened for toxicity, and protective action taken. For example, the toxic stream can be diverted to a temporary holding basin and returned to the waste treatment system at a slower rate to avoid high toxicant concentrations that may otherwise seriously impact wastewater solids quality.
An ideal assessment method for wastewater toxicity is inexpensive, on-line, easy to use, sensitive and relevant to wastewater solids microbial communities. The existing methods of assessing toxicity include: (1) chemical analysis; (2) microscopic analysis; (3) respirometric inhibition methods; and (4) bioluminescence (Kilroy and Gray, 1992).
Chemical analysis of influent wastewater for toxicants requires knowledge of the identity of potential toxicants, is expensive (aton, et al., 1995) and is not rapid enough for effective process control responses. The time available for diversion of toxic influents to holding basins is often on the order of seconds to minutes. Chemical analysis of municipal treatment plant influents is especially problematic due to the complexity and uncertainty of the potential influent toxicants. Microscopic methods for evaluating toxic events are also time consuming because flocs must be examined microscopically. In addition, pin flocs commonly indicative of toxic shock can be caused by other environmental or operating conditions (Jenkins et al., 1993). Microscopic examination of changes in microbial populations or morphology can identify toxic shock, but cannot be used as a preventative method for control of incoming toxic waste streams.
The most common method for assessing wastewater toxicity to wastewater solids is respirometric inhibition (Kong et al., 1996; Strotmann and Eglsaer, 1994). The oxygen consumption rate of the wastewater solids with a wastewater sample is compared to the consumption rate with a non-toxic control. The EC.sub.50 toxicity value is the effective concentration of toxicant for which there is a 50% reduction in oxygen consumption rate (Volskay and Grady, 1988). Decreases in respiration rates indicate toxicity. The respirometry method assesses the metabolic state of the entire community, but is not easily tailored to specific critical populations of potential interest. Determination of toxicity with respirometry can be done on-line, but current technology tends to be expensive and time consuming. In batch grab samples, there is a delay between a toxic compound in the incoming waste stream and the toxicity indication.
The use of bioluminescent microorganisms for toxicity measurements is relatively simple, rapid, does not require chemical identification of the toxic agents and can be used for on-line measurements. Currently available bioluminescent methods to assess ecotoxicity include naturally luminescent marine bacteria, primarily the MICROTOX system (AZUR Environmental), which is considered the benchmark of bioluminescent methods (Paton et al., 1995). This test consists of thawing Photobacterium phosphoreum cells and adding them to a saline buffered, neutral pH solution and measuring the bioluminescent response of the bacteria in a wastewater sample as measured with a luminometer (Dutka et al., 1983). For comparison, the EC.sub.50 value is the concentration of toxicant that results in a 50% reduction in bioluminescence from the baseline level. The inherent difficulties of the MICROTOX system are the requirements for pH and saline buffering, problems with reproducibility (Dutka et al., 1983), its unsuitability for application as an on-line or continuous monitoring system and that the organism is not representative of those species which populate wastewater solids communities.
Another problem of wastewater treatment involves the high cost of disposing of large quantities of sludge. The use of a decoupling agent can reduce sludge volume, but this presents the difficulty of accurately measuring the effect of the decoupling agent on sludge dynamics.
The present invention meets these needs by providing a rapid and effective method for assessing toxicity and for measuring the effect of a decoupling agent in wastewater treatment systems.